Insecticide and method of making same



Patented Sept.

unrro STATES PATENT FFCE.

EDWIN O. BAESTOW AND PAUL COTTRINGER, OF MIDLAND, MICHIGAN, ASSIGNORS TO THE DOW CHEMICAL COMPANY, OF MIDLAND, MICHIGAN, A CORPORATION OF MICHIGAN.

No Drawing INSECTICIDE AND METHOD OF MAKING SAME.

Application filed September.

T 0 all 10]: om it may concern:

Be it known that we, EDWIN O. BAns'row and PA UL Co'i'lm States, and resid Midland. and

NGER, citizens of the United cuts of Midland, count y of State of Michigan, have ointly invented a new and useful Improvement m insecticides and Methods of Making bame,

of which the following is a specificatlon,

the principle of explained and the invention being herein the best mode in which we have contemplated applying that principle, so as to distinguish it from other inventions.

The present improvement relating as indicated to insecticides has regard more particularly to the manufacture of magnesium arsenate or arsenates that will be suitable will be found use. Certain of the adg in magnesium arsenate as well as one method of makin U. S. Patent No. to Edwin O. Barstow (one inventors) under date of June 22nd, 1920.

It has been found, however, in practice that magnesium arsenate when made by dircctly reacting between magnesium hydroxidc Mg(OH).,, and arsenic acid 1s apt to contain more arsenic in soluble form than is desirable.

As a result of further investigation we have accordingly discovered a modified method of manufacture whereby magnesium arsenate may be prepared so as to be substantially free from soluble arsenic. The pr appear to difier particulars from nesium arsenate precise molecular constitution may,

be defined lieve,

oduct thus obtained would in essential and important any known form of mag and irrespective of its we bewith sufficient accuracy to be protected as a part of our invention.

Such invention accordingly consists of the steps and the novel product hereinafter described, it being ticularly facture,

understood, however, paras to such stated method of manuthat changes may be made therein without departing from the spirit of the invention, as also that such product need not necessarily be made by the articular method or methods described herem.

As one illustrative example of the pres ent improved method of manufacture, a

mixture of magn and water conta magnesium hydr into a mixing t esium hydroxide (MgOIL) ining a out six pounds 0 oxide per cubic foot is put ank and to this is slowly 1, 1920. Serial No. 407,449.

added sufficient arsenic acid solution (H AsO to combine with such hydroxide and give the desired strength of arsenic oxide (AS 0 in the final product. It is not necessary to use any particular. strength of magnesium hydroxide or arsenic acid. Usually sufiicient arsenic acid is added to glve a finished product containing 33% of the arsenic oxide but the product may run as high as 40% or even in such oxide. After adding the acid to the mixture of h droxide and water a sample is taken, fi tered, dried and analyzed, and then if the precentage is not as desired, either more magnesium hydroxide or more arsenic is added and this is repeated until the proper analysis is secured.

The mixture resulting from the foregoing step and preferably containing approximately twelve pounds solid per cubic foot of precipitated magnesium arsenate and residual hydroxide is then pumped into an autoclave, there agitated, and heated while under'pressure at a temperature preferably from 165 to 175 C. for a number 0 hours. For operation at the range of temperature just stated, four hours is sufiicient, but if a lower temperature be used, for example, 145 0., a somewhat longer time will have to be allowed for the transformation that attends this stage in the operation. Following the treatment just described, the mixture is then removed from the autoclave, and allowed to settle, followin which it is either filter pressed, dried an ground in a disintegrating type of mill, or after such settling it is fed to an atmospheric drum dryer, where the excess of water is evaporated, giving a dry powder suitable for use as an insecticide.

The final product obtained as. a result of the foregoing consists of a mixture of very fine magnesium arsenate crystals with an excess of magnesium hydroxide present. While the precise composition of such arsenate has not been satisfactorily determined, we have investigated its properties sufiicientl to be convinced that it is essentially di erent from any known form of magnesium arsenate and particularly from that obtained in accordance with the aforesaid Patent No. 1,344,018.

The only magnesium arsenate described in the literature at all fully has a formula MgHAsO,.6-1-2H O (see Abeggs Han buch der. Anorganischen Chemie, 111,? page 541, 1907 Apparently thisis the compound obtained by the patented process except as modified in its roperties by the presence of excess hydroxi e. It occurs in very large flat, plate-like crystals, and shows when tested for solubility by the usual method, from 1.5 to 3% of soluble arsenic oxide (As,O,).

The method of testing arsenates for solubility regularly used is that oflicially prescribed by the Government, in which two grams of arsenate are suspended in one l1ter of pure distilled Water and agitated frequently for twenty-four hours, the arsenic in the solution bein determined after filtration. It has also een usual to test arsenates as to solubility of arsenic content in carbon dioxide. According to this test, the arsenate is suspended in water in the pro portion of two grams per liter and carbon dioxide then passed through. When subjected to this test the old magnesium arsenate will go into solution completely in about an hours time. In other words, with a standard product containing about 33% arsenic oxide, 33% of soluble arsenic will be found after treatment for test. As compared with the foregoing results in the testin of such old magnesium arsenate, the pro uct obtained by the present method when tested for solubility in water invariably shows less than 0.75% of soluble arsenic and frequentl only a mere trace of the latter is foun More strikingly, whenjsubjected to the second test, viz: for solubility of arsenic content in carbon dioxide, 9% represents the maximum solubility of our new roduct containing originally 33% of solub e arsenic.

' In the present new product the magnesium arsenate 15 present in one or all of three distinct crystalline forms. This crystalline material may or may not be mixed with excess magnesium hydroxide, dependin upon the composition of the sample. f the three forms that have been identified the one occurs as exceedingly small, rather lensshaped crystals, having parallel extinction and a negative principal zone, the indices of refraction being as follows, viz: alpha 1.64 and gamma 1.66. The robable formula for this form is MgHAs .mH,,O, in which the value of at has not been definitely determined as yet. A second form occurs either as long, needle-shaped crystals, elongated, pointed-ended crystals, or short, fiatended prisms, having parallel extinction and a positive princi a1 zone, the indices of refractlon being as ollows, viz: alpha 1.58 and gamma 1.605. The probable formula for this form is Mg,,(AsO .MgO.g H O', in which the value of g has not yet been definitely determined. The third form is piobably re resented by the formula (AsO,,) .2 g O.zI-I,O, in which the masses value of 2 has not yet beendefinitely determined. This form occurs as exceedin ly small, lens-shaped crystals, having parafiel extinction and a positive principal zone, the indices of refraction being as follows, viz: al ha 1.565 and gamma 1.575.

n addition to. the magnesium arsenate hereinbefore referred to as described in the literature, viz: the acid arsenate with 6% molecules of water, a second form of such arsenate has been identified as occurring in the mineral Hoernesite having the formula Mg,,(AsO,) .8H,O. We have definitely established that the arsenates occurring in the present new compound contain much less than this amount of crystal water. Magnesium pyro-arsenate with the formula Mg,,As.,,O is also described in the literature and has been repared, but this compound possesses no efinite crystalline structure and shows a soluble arsenic content, when tested by the usual method, of more than 5%.

In view of the foregoing it is believed that the compounds occurring in the new magnesium arsenate obtained by the process hereinbefore described have never before been made or described. Indications of the presence of one or two compounds in addition to those described above have been obtained in certain samples of the new material but one or the other of the three products noted above apparently make up the bulk of the product.

As an indication of the variations that may be made in the specific illustrative process described, it should be stated that the admixture of the arsenic acid to the suspended magnesium hydroxide may, if found desirable, take place in the autoclave, thus combining both steps of the described proc-- ess in one. Furthermore, the magnesium hydroxide, suspended in a slurry, may be added to the acid, either as separately in advance to the autoclave step, or, as just indicated, such addition may take place in the autoclave at once.

It will also be understood that magnesium oxide (MgO) may be substituted for magnesium hydroxide in any of the foregoing methods of reparation, as also that the arsenate may be formed by a so-called decomposition, i. e. by the reaction of a soluble arsenate with a soluble magnesium salt. Thus sodium arsenate and magnesium chloride may be caused to react in accordance with the following equation, viz:

The autoclaving, just as before, may be carried out incidentally to the reaction or subsequently thereto i. e. after the precipitate of magnesium arsenate has been formed. We have also found it possible to obtain satisfactory results by utilizing a messes waste product which contains arsenic acid and sodium arsenate, adding thereto magnesium h droxide to combine with such arsenic acid and magnesium chloride to react with the sodium arsenate, then washing to remove the sodium chloride formed, and heating the resulting product in an' autoclave under pressure, there being referably an excess of magnesium hydroxi e present.

Other forms may be employed embodying the features of our invention instead of the one here explained, change being made in the orm or construction, provided the elemerits stated by any of the following claims, or the equivalent of such stated elements be employed, whether produced by our preferred method or by others ,embodyin steps equivalent to those stated in the following claims.

We therefore particularly point out and distinctly claim as our inventlon 1. In a method of making magnesium arsenate, the steps whichconslst in causing a reaction between arsenic acid and a magnesium compound capable of forming the arsenate therewith, andsubjecting the resulting mixture in an autoclave to a temperature above the boiling pint of water.

2. In a method of ma mg magnesium arsenate, the steps which consist in causing a reaction between arsenic acid and a magnesium compound capable of forming the arsenate therewith, and subjecting the resulting'mixture in an autoclave to a temperature of from 145 to 175 C.

3. In a method of making magnesium arsenate, the steps which consist in causing a reaction between arsenic acid and a magnesium compound capable of forming the arsenate therewith, and subjecting the re-- sulting mixture in an autoclave to a tem-' perature'above the boiling point of water while under a pressure greater than atmospheric'.

4. In a method of making magnesium arsenate, the steps which consist in causing a reaction between arsenic acid and ma nesium hydroxide, and subjecting the resufiing mixture in an autoclave to a temperature above the boiling point of water.

5. In a method of making magnesium arsenate, the steps which consist in causing a reaction between arsenic acid and magnesium hydroxide, and subjecting the resulting mixturein an autoclave to a temperature of from 145 to 175 C. a i

6. In a method of making magnesium arsenate, the steps which consist in causing a reaction between arsenic acid and m nesium hydroxide, and subjecting the resul iii ing mixture in an autoclave to a temperature .resulting mlxture under pressure.

8. In a method of making magnesium arsenate, the steps which consist in addin a solution of arsenic acid to an excess o magnesium hydroxide suspended in water, heating the resulting mixture under pressure, separating and drying the solid material then remaining, and pulverizing the same.

9. As a new roduct, a compound suitable for insecticidal use containing magnesium arsenate in highly insoluble form, less than 1.00% soluble arsenic being found in a sample suspended inwater and agitated for a period of twenty four hours.

10. As a new product, a compound suitable for insecticidal use containing magnesium arsenate in highly insoluble form, not more than 0.75% soluble arsenic being found in a sample suspended in water an agitated for a period of twenty four hours.

11. As a new product, a compound suitable for insecticidal use containing magnesium arsenate in highly insolublecrystalline form, the. crystals being exceedingly small and having parallel extinction and either a negative or osit-ive principal zone.

12. As a new pro not, a compound suitable for insecticidal use contaming magnesium arsenate in highly insoluble crystalline form, the crystals being exceedingly small and lens-shaped, and having parallel extinction and either a negative or posltive principal zone.

13. As a new product, a compound sultable for insecticidal use containing -ma nesium arsenate in highly insoluble crysta line form, the crystals being exceedingly small and having indices of refraction lying between the following limits, viz: alpha 1.56 to 1.64 and gamma 1.57 to 1.60.

14. As a new product, a form of ma nesium arsenate having the general formu a MgHAsO,.:vH O, occurring as exceedingly small, rather lens-shaped crystals havm parallel extinction and a negative princi' a zone, the indices of refraction being as 01- lows, viz: alpha 1.64 and mma 1,66.

Signed by us at Midlan Mich, this 25th day of August, 1920.

EDWIN O. BSTOW..

PAUL COTTRINGER. 

